1. Field of the Invention
The present invention relates to a finisher for finishing sheets for use in a copier, printer or similar image forming apparatus and, more particularly, to a finisher having a sorter for sorting sheets for a plurality of bins, and further having a stapler or a punch device.
2. Description of the Prior Art
Recently, various finishers which use helical cam shifts and have a plurality of bins moveable in the vertical direction have been proposed.
In the above-mentioned finisher, the space between a bin and an adjacent bin is relatively narrow in a waiting condition of an image forming apparatus, and the space between the first bin moved to the position at which image formed sheets are discharged and the second bin located at the position just above the first bin (such finisher being described in Japanese patent application Laid Open No. 64-64973/1989) is relatively broad in a sheet discharging condition.
A sufficient space between the top sheet in the bin for discharging sheets and the bin located at a position above the top sheet is necessary for accurately positioning the discharged sheets in the bins. If not enough space is provided, it is difficult to attain accurate positioning of the discharged sheets in the bin for discharging sheets. Because the curled sheet relatively forcefully touches the top sheet or the bin located at the position above the top sheet, it makes it difficult for sheet discharge into the preferred position of the bin. Furthermore, movement of the discharged sheet on the top sheet by a jogger is relatively difficult from the discharged position to a predetermined position.
On the other hand, in a sorter having the moveable bins, it is necessary that the next bin be moved to the sheet discharging position by completion of the period during which the next sheet may be discharged after the finished sheet is discharged into the bin.
FIG. 1 is a timing chart concerning bin movement and jogger movement of a prior art apparatus. In the figure, the jogger is the device for aligning sheet sides in the bin "T.sub.1 " (sec) shows the sheet discharging cycle, in which the sheet discharging is detected by a sensor, and "t" shows the period during which the discharging sheet drops into the bin and the sheet is moved to the end edge portion of the bin. The bin which is located at the discharging position has a space with a dimension of "45" mm in the upward direction of the bin and then the bin is moved up to the not-discharged position, wherein the space is "15" mm which is the regular spacing. The corresponding CPM (copying per minute) of the image forming apparatus is 60/T.
In order to attain high-speeding operations of the finisher, it is possible to perform the following steps.
(1) decrease the moving time of the bins PA1 (2) decrease the operation time of the jogger PA1 (3) speed up sheet discharging to the bin
However, each step has the following shortcomings: As for item (1), it is necessary to employ an expensive motor. As for item (2), it is difficult to perfectly align the sides of the discharged sheet and as for item (3), the sheets are incorrectly stacked so that the sheets are aligned in a disorderly manner.
Furthermore, in order to attain high-efficiency operations of the finisher, it is possible that the finisher causes the jogger to align the sheets and thereby the bin moves at the same time.
However, if the bin space located over or under the bin, into which sheets are discharged, is established so as to be the same as the space formed by each of the other bins, the space which is formed by each of bins changes so as to be narrower corresponding to the bin's movement (for example, the space changes from 45 mm to 15 mm). This narrow space causes the side of the stacked sheets to be aligned in a disorderly manner, because the discharged sheets abut against the bins.